| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug capable of effectively burning out carbon adhered onto an outer peripheral surface of an insulator by generating a leakage current between a shelf part of a housing and the outer peripheral surface of the insulator.SOLUTION: A spark plug 1 comprises: a cylindrical housing 2 provided with a ground electrode 21; a cylindrical insulator 3 inserted into an inner peripheral side of the housing 2; and a center electrode 4 inserted into an inner peripheral side of the insulator 3. The housing 2 has a shelf part 22 formed by diameter reduction of a part in a central axis line direction O, of its inner peripheral surface 201. The insulator 3 has a step surface 33 between a front end side insulator part 31 and a rear end side insulator part 32. An annular packing 5 is held between a rear end side end surface 221 of the shelf part 22 and the step surface 33. On an inner peripheral surface 201 of the shelf part 22, an unevenness 23 whose gap from an outer peripheral surface 301 of the insulator 3 changes is repeatedly formed at a plurality of points in a circumferential direction. |
